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Checker Glossary

AVL storage#

AVL tree (named after inventors Adelson-Velsky and Landis) is a self-balancing binary search tree. In Checker, AVL trees are used to keep track of:

  • Liquidation slices queued for an auction
  • Liquidation slices in the current auction
  • Liquidation slices in completed auctions

The AVL tree for the queued liquidation slices always has the root 1. In our cCHF contract, the AVL tree is stored in liquidation_auctions>avl_storage>mem.

Burrow (Vault)#

A contract for a “deposit account” that supports a few operations, e.g. “minting” (ie. borrowing) kit, or “burning” (ie. repaying) kit. A fresh burrow contract is created for every depositor, and only Checker is allowed to access it, so operations on burrows are performed via the Checker contract. In accordance with the existing Youves Synthetic Asset engines, the term "burrow" is synonymously used for "vault". More information here.


Checker is a generic piece of software for creating robocoins on the Tezos blockchain. It is an open source project supported by Nomadic Labs, Tweag and TZ Connect Berlin. cCHF is an implementation of Checker, which is tracking the price of the Swiss Franc. An in-depth documentation of checker can be found here.


Drift is a dynamic parameter which varies continuously over time used for adjusting the quantity. It represents the growth or shrinking of the quantity per unit of time. More information here.


The ratio of the number of circulating kits to the number of outstanding kits.

Imbalance adjustment#

A compounding fee or reward applied to burrows which implicitly increases or decreases the number of outstanding kit over time to bring it closer to the number of circulating kits so as to bring the imbalance closer to 1.

Kit (cCHF)#

A coin / token created and destroyed as part of the system. cCHF is our name for kit.

Liquidation auction#

In Checker, liquidation auctions are being used to auction off slices of collateral of undercollaterlized burrows (vaults). Liquidation auctions are an integral part of Checker.

Only one auction can take place at any time. It is referred to as the current_auction in the contract's storage. In our cCHF contract, details about the current liquidation auction can be viewed in the contract view: current_liquidation_auction_details. A liquidation auction is used to auction off collateral of overburrowed vaults for kit (cCHF).

Circulating kit#

The amount of kit (cCHF) that exist.

Outstanding kit#

The amount of kit (cCHF) that it would take to close all currently open burrows.

Liquidation lot#

A batch of liquidation slices being auctioned of in the current auction.

Liquidation queue#

A queue implemented as a balanced binary tree representing an ordered list of liquidation slices. Slices at the front of the queue are periodically batched into a liquidation lot.

Liquidation slice#

Some amount of collateral (tez), tied to a burrow, which is inserted in the liquidation queue to be auctioned off for kit.


In the context of Checker overburrowed is synonymous to undercollateralized. A burrow (vault) being overburrowed means that it's owner has minted more kit than the burrow's collateral would allow him to at the moment of observation. Or in different words: The burrow has not enough collateral to meet the collateral requirements of Checker. A user can choose to deposit more collateral or repay (burn) kit (cCHF) in order to avoid being partially liquidated.


The quantity is a time-dependent property of the system which can fluctuate upwards or downwards. More information here.